The invention relates generally to organic rankine cycle (ORC) systems, and more particularly to an economical system and method for the same.
With the advent of the energy crisis and, the need to conserve and more effectively use our available energies, rankine cycle systems have been used to capture the so called “waste heat,” that was otherwise being lost to the atmosphere and, as such, was indirectly detrimental to the environment by requiring more fuel for power production than necessary.
Common sources of waste heat that are presently being discharged to the environment are geothermal sources and heat from other types of engines such as gas turbine engines, that give off significant heat in their exhaust gases, and reciprocating engines, that give off heat both in their exhaust gases and to cooling liquids such as water and lubricants.
In general, ORC systems have been deployed as retrofits for small and medium-scale gas turbines, to capture from the waste heat gas stream desirable power output. A working fluid used in such cycles is typically a hydrocarbon at about atmospheric pressure. However, the working fluid may degrade beyond a critical temperature, such as, but not limited to, 500 deg C. In a gas turbine system, the temperature of the exhaust is comparable to such high temperatures and hence, there is a reasonable probability of degradation of the working fluid due to direct exposure to the waste heat gas from the exhaust.
In order to avoid the aforementioned issue, an intermediate thermal fluid system is generally used to convey heat from the exhaust to an organic Rankine cycle boiler. In an example, the fluid is oil. However, the intermediate thermal fluid system represents up to about one-quarter of the cost of the complete ORC. Furthermore, the intermediate thermal fluid system and heat exchangers require a higher temperature difference resulting in an increase in size and a lowering of the overall efficiency.
Therefore, an improved ORC system is desirable to address one or more of the aforementioned issues.